V Subramanyan: Mumbai needs to fix its buildings

An earthquake of magnitude 6.9 rocked Sikkim on Sunday, nearly 31 years after the last big quake of magnitude 6.1 in November 1980. The loss of life was minimal for a quake of such magnitude since it struck remote, less inhabited areas, but hundreds of buildings all over Sikkim were reportedly damaged.

In all probability, these dwellings were not built to standard specifications for earthquake resistance keeping in mind the high seismicity of the region (zone 4). Collapsing buildings during earthquakes are the only reason for the large number of deaths.

This was demonstrated amply during the Killari earthquake of September 30, 1993, of magnitude 6.2, when more than 10,000 sleeping villagers never saw the light of day in Latur and Osmanabad districts of Maharashtra, their houses having been built of just piled boulders collected from the fields.

Quakes are the most disastrous of all Nature’s weapons of mass destruction, wreaking large-scale havoc in a matter of seconds, and there is no stopping them, or even predicting them with any degree of certainty. To add to the complexity of the phenomenon, newer places hitherto considered immune to earthquake occurrence, like New York, have become vulnerable.

The only way to survive an earthquake is through appropriate construction of buildings. Any compromise on this score could prove fatal. A lot of research has gone into this aspect, with valuable inputs from the US and Japan, the two leading nations most prone to seismic events. So, today, several authentic designs are available to erect buildings in a way that they will not be pulled down when a quake’s vibrations pass through their foundations.

They cost just 10% more than the overall cost of the buildings, but it is money well spent considering that this extra expenditure can ensure our safety like nothing else. There are ways to strengthen existing buildings as well, called ‘retrofitting’.

Since the Sikkim quake has affected far-off places like Delhi, Patna, Kathmandu and Kolkata, the nature of buildings in these places needs to be examined from this point of view and appropriate reinforcements provided where necessary.

This is applicable to Mumbai as well, which lies in a moderately seismic zone. Though the region has not had a major quake after 1993, it has had a few minor shocks of magnitude up to 4 in the past 10 years, mostly at places like Taloja and Kalyan to the east of the Thane creek.

The last one occurred at Thane in August 2010. This is an indication that the seismic activity that has so far been confined to the region to the east of the creek is trying to make its presence felt in the island of Mumbai.

Therefore, seismic retrofitting in all residential buildings, particularly those in the eastern suburbs, is called for. It would, of course, be good to extend this safety measure to buildings in South Mumbai as well, particularly those between Malabar Hill and Worli where a long geological fault grazing past the Malabar-Cumballa-Worli hills complex had been reported in 1968.